The almost complete transition from porcelain to polymeric housings in MV arresters over a period of only a decade has been nothing short of extraordinary. This is particularly so if one considers that acceptance of new technologies is generally quite a slow process by what is a very conservative customer base.
Nevertheless, what drove this transition forward in the case of distribution was the almost universally-acknowledged unsatisfactory performance of porcelain-housed designs which were subject to frequent problems of moisture ingress, often resulting in explosive shattering. Safety to people in neighbourhoods through which distribution lines passed was therefore an important consideration.
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| Test set-up to evaluate performance of polymeric arrester at German substation. |
In the case of arresters for HV station applications, however, this type of situation has definitely not been the case. "the market for MV arresters was driven to polymers by safety considerations. However, in the case of HV arresters, these have been designed to always handle internal failure without catastrophic consequences. Basically, the porcelain in these designs has the integrity to withstand any internal faults without explosive shattering."
Any criticism of porcelain station arresters for exploding and causing damage to surrounding equipment is unfair and probably just not correct .If there have been such cases, these have most likely been due to misapplication since every station arrester has a pressure relief mechanism. If it fails, it should vent successfully.
Explosive failures of porcelain HV arresters have sometimes occurred when a network has been upgraded without replacing the pre-existing arresters. Whenever there is an upgrade at a station, it is important to look at the nameplate in order to review the pressure relief behaviour of the existing arresters for any increase in their short circuit rating."
During the past 20 years the pressure relief ratings of most porcelain station arresters have more than doubled. Older models of such arresters therefore may not always be designed to deal with the available fault current at a station after an upgrade. In this respect, it is perhaps true to say that a polymeric HV arrester is safer than a misapplied porcelain HV arrester.
